What you aren't ready for being the first time in space - on an emotional and intellectual level - is how looking down at Earth will profoundly affect you. Over the long term, it has changed the way I think about planet Earth. When you go around the planet and look down, you think about the fact that this is the cradle of humanity, that this is a place where seven billion people, 200 countries, live side by side, that we share this place and there's nowhere else to go.